Inkjet printers eject liquid ink droplets onto a recording medium, such as paper, from a printhead that moves relative to the recording medium and/or vice-versa. A printhead generally comprises one or more fluid ejection chips, each including a semiconductor substrate upon which one or more fluid actuator devices, such as electrical heater elements, are disposed for transferring thermal energy into liquid ink. The liquid ink is heated such that a rapid volumetric change occurs in the ink resulting from a liquid to vapor transition and, consequently, the ink is forcibly ejected from the printhead as an ink droplet onto a recording medium.
As inkjet printheads are often subject to repeated and/or long-term use, a printhead typically includes a replaceable and/or replenishable ink reservoir, such as a cartridge, tank, bladder, or other volume for storing liquid ink. Over time, pigment within the ink stored in the reservoir may settle, resulting in varying concentrations of ink in the droplets ejected by the printhead. This results in inconsistent performance of the inkjet printing system.